1. Field of the Invention
The invention generally relates to WLAN (Wireless Local Area Network) communication devices, integrated circuit chips, memory devices and corresponding methods, and more particularly to techniques for controlling access to an on-chip memory.
2. Description of the Related Art
A wireless local area network is a flexible data communication system implemented as an extension to or as an alternative for a wired LAN. Using radio frequency or infrared technology, WLAN systems transmit and receive data over the air minimizing the need for wired connections. Thus, WLAN systems combine data connectivity with user mobility.
Today, most WLAN systems use spread spectrum technology, a wideband radio frequency technique developed for use in reliable and secure communication systems. The spread spectrum technology is designed to trade-off bandwidth efficiency for reliability, integrity and security. Two types of spread spectrum radio systems are frequently used: frequency-hopping and direct sequence systems.
The standard defining and governing wireless local area networks that operate in the 2.4 GHz spectrum is the IEEE 802.11 standard. To allow higher data rate transmissions, the standard was extended to 802.11b which allows data rates of 5.5 and 11 Mbps in the 2.4 GHz spectrum. Further extensions exist.
When using wireless communication techniques, various data encryption schemes may be applied. For instance, AES (Advanced Encryption Standard) is a data encryption scheme which uses three different key sizes (128-bit, 192-bit, and 256-bit) but only one encryption step to encrypt data in 128-bit blocks. The AES mechanism is based upon the Rijndael algorithm.
Another data encryption scheme that may be applied in wireless communication systems is TKIP (Temporal Key Integrity Protocol) which is part of the IEEE 802.11i encryption standard for WLAN systems. TKIP is the next generation of WEP (Wired Equivalency Protocol) which is used to secure 802.11 wireless networks. TKIP provides per-packet key mixing, a message-integrity check, and a re-keying mechanism.
When using modern wireless communication systems, for instance those which are 802.11b/i compliant, the devices need to meet the protocol timing even when using slow target interfaces such as SDIO (Secure Digital Input/Output) or CF (Compact Flash). SD cards are small media-type devices that have extra connections to secure data. SDIO slots accept not only memory but also expansion hardware for Bluetooth, wireless communications, and other purposes. CF is a 50-pin connection standard used in some PDAs (Personal Digital Assistants), digital cameras, hardware MP3 (MPEG-1 layer 3 audio encoding, Motion Picture Expert Group) players and other small devices. It was initially designed to offer PCMCIA-ATA (Personal Computer Memory Card International Association, Advanced Technology Attachment) standard access to flash memory in a smaller form factor. The standard is now also used for other purposes.
For bringing together fast timing schemes (such as those which are 802.11b/i protocol compliant) with slow target interfaces (such as SDIO, CF and others), data buffering is an option to match diverging requirements. Various techniques are available which could in principle be used for this purpose.
FIG. 1a schematically shows a typical RAM (Random Access Memory) device.
FIG. 1b shows a dual-port RAM which has two independent write/read ports that allow multiple reads or writes to occur at nearly the same time. However, dual-port RAM devices tend to have lower capacity, to need large chip areas, and to suffer from severe power consumption.
Thus, the existing convention techniques may have problems in that they either cannot provide the performance, operating speed and efficiency needed to comply with the requirements (in particular when using single-port devices), or they require high chip area and lead to high power consumption, thereby increasing the manufacturing and development costs (for instance when using dual-port devices or even multi-port units that have more than two ports). Moreover, the prior art techniques are often much too inflexible to allow for meeting the data throughput constraints given by modern applications. Thus, conventional techniques often do not allow for sufficiently compensating interface latencies.